Properties of nanocrystalline Al–Cu–O films reactively sputtered by DC pulse dual magnetron

The article reports on the effect of the addition of copper in the Al₂O₃ film on its mechanical and optical properties. The Al–Cu–O films were reactively co-sputtered using DC pulse dual magnetron in a mixture of Ar + O₂. One magnetron was equipped with a pure Al target and the second magnetron with a composed Al/Cu target. The amount of Al and Cu in the Al–Cu–O film was controlled by the length of pulse at the Al/Cu target. The Al–Cu–O films with ≤16 at.% Cu were investigated in detail. The addition of Cu in Al₂O₃ film strongly influences its structure and mechanical properties. It is shown that (1) the structure of Al–Cu–O film gradually varies with increasing Cu content from γ-Al₂O₃ at 0 at.% Cu through (Al_8−2x,Cu_3x)O₁₂ nanocrystalline solid solution to CuAl₂O₄ spinel structure, (2) the Al–Cu–O films with ≥3 at.% Cu exhibit (i) relatively high hardness H increasing from ∼15 GPa to ∼20 GPa, (ii) enhanced elastic recovery W_e increasing from ∼67% to ∼76% with increasing Cu content from ∼5 to ∼16 at.% Cu and (iii) low values of Young's modulus E* satisfying the ratio H/E* > 0.1 at ≥5 at.% Cu, and (3) highly elastic Al–Cu–O films with H/E* > 0.1 exhibit enhanced resistance to cracking during indentation under high load.